The prior art is replete with actuating mechanisms for imparting oscillatory motion to an output shaft journalled for pivotal movement about a fixed pivot axis. Such mechanisms have particular utility in vehicle windshield wiper systems in which a wiper blade is oscillated through a wipe pattern.
Most windshield wiper mechanisms utilize a rotary crank as part of the linkage between a drive motor and the output shaft. A desirable feature of such systems is the ability to shift the wiper blade to a depressed "Park" position outside of the normal wipe pattern when the wiper mechanism is inoperative. This frequently is accomplished by provision of a means for varying the throw of a rotary crank upon reversal of the direction of rotation of the drive motor coupled to the crank. Rotary movement of the crank is translated into oscillatory movement of the pivot shaft through a suitable linkage system.
Patents that are representative of the prior art include U.S. Pat. No. 2,831,354 issued Apr. 22, 1958 to William A. Schnepf for a "Windshield Wiper Actuating Mechanism." This patent discloses a mechanism utilizing a screw element operatively connected through an automatically disengageable and engageable clutch to the wiper transmission. Through the screw element and clutch, the effective length of the crank may be varied so as to alter the amplitude of oscillation imparted to a driven member.
U.S. Pat. No. 3,091,128 issued May 28, 1963 to D. D. DeReese et al. for a "Windshield Wiper Mechanism" discloses a mechanism wherein the throw of the rotary crank is varied by eccentric means controlled by an electromagnet. U.S. Pat. No. 2,768,530 issued Oct. 30, 1956 to A. D. Brundage for a "Windshield Wiper Drive and Parking Control" discloses a system involving an eccentric operative to increase the effective length of the crank arm upon reverse rotation of a motor shaft, the position of the eccentric being mechanically controlled.
It is an object of the present invention to provide a novel actuating mechanism for imparting oscillatory motion to an output shaft, the mechanism having the capability of shifting the oscillation pattern in direct response to a change in direction of rotation of a drive motor without the use of any type eccentric device for changing the effective length or throw of a rotary crank.